Glial-derived neurotrophic factor reduces inflammation and improves delayed colonic transit in rat models of dextran sulfate sodium-induced colitis,☆☆

https://doi.org/10.1016/j.intimp.2014.01.008Get rights and content

Highlights

  • GDNF ameliorates significantly gut dysmotility in DSS-induced colitis.

  • GDNF prevents partially the loss of enteric neurons by inhibition of enteric neuronal cell apoptosis.

  • GDNF down-regulates TNF-α and IL-1β expression and the infiltration of leukocytes.

  • GDNF improves significantly experimental colitis.

  • GDNF may be a useful therapeutic agent for the treatment of gut dysmotility in patients with UC.

Abstract

Background

Intestinal inflammation is well known to cause gut dysmotility through the effects on the enteric nervous system. Glial-derived neurotrophic factor (GDNF) has been demonstrated to have anti-inflammatory effects and neuronal protective actions. The aim of this study was to investigate whether the GDNF could improve inflammation-induced gut dysmotility.

Methods

Recombinant adenoviral vectors encoding GDNF (Ad-GDNF) were administered intracolonically in experimental colitis induced by dextran sulfate sodium (DSS). The disease activity index (DAI) and histological score were measured. Colonic transit was measured by using phenol red and assessed with the geometric center. PGP 9.5 immunostaining was used to examine the number and distribution of enteric neurons. The expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and myeloperoxidase (MPO) activity were measured by ELISA assay. The expression of Akt, caspase-3, bcl-2 and PGP 9.5 was analyzed by western blot assay.

Results

A significant neuronal cell loss and a significant delay in colonic transit accompanied with the neuronal loss following inflammation were observed. GDNF prevented partially the loss of enteric neurons and ameliorated significantly experimental colitis and delayed colonic transit by, at least in part, down-regulation of TNF-α and IL-1β expression, decrease of infiltration of leukocytes, and inhibition of neuronal cell apoptosis.

Conclusions

GDNF reduces inflammation and improves delayed colonic transit in DSS-induced colitis. GDNF may be a useful therapeutic agent for the treatment of gut dysmotility in patients with UC.

Introduction

Colonic dysmotility is a common complication of ulcerative colitis (UC), which is a chronic and relapsing intestinal inflammatory disorder primarily involving in the colon [1], [2]. Previous studies have demonstrated that colonic motility is impaired in patients with UC [1], [2], [3], [4], and it is well known that the development of gut dysmotility may increase the potentiality for bacterial overgrowth and lead to a translocation of bacteria and/or bacterial toxic products through the intestinal mucosal barrier, thereby increasing the severity of gut injury, which in turn aggravates the gut dysmotility [4], [5]. Such an event probably produces an insidious cycle, which may play an important role in the pathogenesis of UC. Accordingly, the effective therapy for gut dysmotility in UC is of clinical significance. However, the therapies for this motor disorder have usually been overlooked clinically, and more importantly, no definitive therapies are available for this motor disorder because the exact mechanisms causing gut dysmotility in UC are unknown. Therefore, a better understanding of the mechanisms underlying the gut dysmotility that occur in patients with UC and the development of new therapeutic strategies to treat this condition are of great clinical significance.

It is well recognized that gastrointestinal motility is altered in patients with UC [1], [2], [3], [4], but the mechanisms that are responsible for gut dysmotility remain controversial but likely involve inflammation [6], [7], [8], [9], [10], [11]. In fact, a variety of studies from humans and animal models consistently indicate that there is a causal relationship between the presence of gastrointestinal inflammation and gut dysmotility [6], [7], [8], [9], [10], [11]. Indeed, a number of previous studies have demonstrated that inflammatory conditions which are characterized by the recruitment of leukocytes and the local generation of pro-inflammatory mediators including various cytokines, nitric oxide, and prostaglandins within the gut tissues are involved in the pathogenesis of gut dysmotility [1], [12], [13], [14]. Nevertheless, although the concept that inflammation alters gut motility is now well accepted, little is known about the exact mechanisms involved in gut dysmotility occurring in mucosal inflammatory conditions. Recently, a growing body of evidence indicates that mucosal inflammation of the gut causes structural and functional changes to the enteric nervous system (ENS) including changes in the content of neurotransmitter and neuronal numbers and so on [15], [16], [17], [18]. It is well known that ENS is an integrative neuronal network localized in the wall of the gastrointestinal tract and regulates and controls almost all aspects of gut function including gut motility [17], [18]. It is therefore perhaps not surprising that gastrointestinal inflammation-induced dysmotility is largely due to structural and functional alterations in the ENS that occur in mucosal inflammatory conditions. Indeed, abundant studies have shown that there are significant impairments in gut motility including propulsive, contractile and transit function accompanied with transient or even permanent structural and functional alterations in the ENS follow inflammatory response [7], [19], [20], [21]. The inflammation usually diffuses into the mucosa/submucosa and muscle layer and induces gut dysmotility after the initiation of mucosal inflammation. Overall, these data indicate that inflammation-induced alterations in the ENS play an important role in the pathogenesis of gut dysmotility. Therefore, the effective inhibition of gut inflammatory response might be of therapeutic potential for gut dysmotility that is associated with inflammation. Indeed, previous studies had shown that the administration of anti-neutrophil serum or steroids attenuated effectively the inflammatory response, partially reduced the extent of myenteric plexus neuronal cell loss, and improved the impairment of gut motility in murine models of colitis [21], [22].

Glial-derived neurotrophic factor (GDNF) produced by enteric glial cells is an important neurotrophic factor for the ENS. It was reported that GDNF has a prominent role in promoting the development and survival of enteric neurons [23]. Furthermore, our earlier findings and the findings of other investigators had shown that GDNF was able to inhibit the mucosal inflammatory response of gut and reduce loss of neurons by protecting neurons from apoptosis [23], [24], [25]. More importantly, a recent study from Anitha et al. had demonstrated that the administration of GDNF improved gastrointestinal motility disorder in diabetic mice [26]. Conversely, the absence of GDNF receptor alfa2 caused the impairment of small bowel transit in mice [27]. In addition, the selective ablation of enteric glial cells, which are well recognized to be sources of GDNF, by a gliotoxin also resulted in intestinal dysmotility in rats [28]. Taken together, these data suggest that GDNF is involved in the modulation of enteric neural pathways responsible for the control of the motility of the gastrointestinal tract. Therefore, it could be speculated that GDNF may be developed to a potential therapeutic approach in treatment for motor disorders of patients with UC. Unfortunately, to date, there has been no information on whether GDNF is therapeutic for gut dysmotility in patients with UC. We therefore hypothesized that GDNF could improve gut dysmotility by its anti-inflammatory effect and neuronal protective actions. Here, we investigated whether the inflammatory response was responsible for the impairment of gut dysmotility and whether the GDNF could improve the gut motility disorder in a murine model of dextran sulfate sodium (DSS)-induced colitis, which resembles human UC, in order to provide experimental evidence that GDNF serves as a possible treatment for motor disorders of the gastrointestinal tract in patients with UC.

Section snippets

Animals

Male Sprague–Dawley rats weighing 200–250 g were obtained from the Experimental Animal Center of Sichuan University, Chengdu, China and housed in microisolator cages at room temperature (25 °C) and humidity 40% with alternating 12:12-h light-dark cycles. Rats had free access to regular chow pellets and drinking water. Before the experiments, all rats were starved overnight with free access to water. This study was approved by the Animal Ethics Committee of West China Hospital, Sichuan University.

Construction of the recombinant adenoviral vectors encoding GDNF (Ad-GDNF)

Effects of GDNF on clinical indices and histological injury scores

Treatment with Ad-GDNF significantly ameliorated experimental colitis as assessed by DAI and histological injury scores. As shown in Table 1 and Fig. 1, compared with the normal control group, the DAI scores were increased markedly in rats from the DSS group (P < 0.05). In contrast, treatment with Ad-GDNF significantly reduced the DAI scores in rats with DSS-induced colitis. Consistent with the clinical features, administration of Ad-GDNF led to a significant improvement in the histological

Discussion

Our data demonstrated a significant neuronal cell loss following DSS-induced colitis, and a significant alteration in colonic transit accompanied with the neuronal loss which was associated with neuronal cell apoptosis. Importantly, we demonstrated that GDNF prevented partially the loss of enteric neurons and ameliorated significantly delayed colonic transit and DSS-induced colitis. The beneficial effect of GDNF treatment could be linked, at least in part, to the down-regulation of TNF-α and

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    The present work was supported by the National Natural Science Foundation of China (No. 81170369) and the Science Foundation from the Science and Technology Department of Sichuan Province, PR China (No. 2011SZ0199).

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    All authors state that no conflicts of interest (including financial, professional, or personal conflicts) exist.

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